I hope you still have the System disk that came with that iMac. I say this because written small on one of the disk is the words "Hardware Tests". Then you could boot to that disk and run the hardware tests to see if it catches anything.

I have a 2008 20" iMac. Leopard snow. It can be on for 3 days and shut off if I move the mac to show the screen to someone, or it can be on for 5 minutes and not even touching it, like today and it shuts off. Too make it worse, when it does, I have to use Disk Warrior to rebuild the disk. Every time. it always says my keys are out of order.

If I shut it off myself, it always starts, when it crashes like that it never restarts. Any suggestions?

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